1. Field of the Invention
Embodiments disclosed herein relate generally to containers for storing and transporting drilling waste. More specifically, the present invention relates to skips for storing and transporting drill cuttings and substances produced in the course of offshore drilling operations.
2. Background Art
FIG. 1 shows a typical offshore drilling rig 100 having a derrick 102, a floating platform 104, and a riser 106 that extends from the offshore drilling rig 100 down to the seabed 110. In drilling operations, particularly in the drilling of oil and gas wells large amounts of waste material is generated when drilling a wellbore 108 in an earth formation. The waste material generated is also known as drill cuttings. Drill cuttings may comprise, for example, rock, dirt, shale, and other debris. Drilling fluid (“drilling mud”) is often pumped downhole for a number of different purposes, such as lubrication of the drill string within the riser 106, prevention of corrosion, and transport of drill cuttings to the surface. Drilling fluid may be oil or water-based, although oil-based drilling fluids are preferred in lower sections of bore, and are also generally less costly than water-based drilling fluids.
Once the drilling fluid is returned to the surface, it is passed through screens, vibratory separators, or other filtering arrangements to separate the waste material and drill cuttings from the drilling fluid. The drilling fluid may then be sent to a reservoir or returned to the system and reused. Drilling cuttings processed by filtering arrangements may contain approximately 10% to 20% moisture (oil, water) by weight. Because the waste material and drill cuttings contain contaminants, such as chemicals, hydrocarbons such as oil and other components hazardous to the environment, environmental regulations require that the waste material and drill cuttings be processed and disposed of in an environmentally acceptable manner. Contaminated waste material and drill cuttings recovered from an offshore drilling rig typically require removal from the rig or wellbore for treatment on land to decontaminate them before they can be safely disposed.
The waste material and drill cuttings are collected and stored on the drilling platform 114 or vessel in small containers, also known as mud skips, skips, or cuttings boxes, before being transported onshore for processing. The skips may be lifted by a crane 112 and loaded on a ship 116, or supply boat, for transportation to a shore base facility. The skips typically have about a five ton capacity and a typical drilling operation may produce up to 800 ton of drilling waste. Many skips are necessary on a typical drilling rig to handle the large amounts of drill cuttings generated. Dedicated crews are necessary to handle the skips on the drilling and at the shore base facility, cleaning crews are necessary to clean the skips after each use, and crews are needed to address safety and environmental concerns in each operation handling the skips.
FIGS. 2 and 3 show examples of typical mud skips 220 having a lid 222 coupled to the top 224 of the tank 220. A plurality of lifting eyes 228 are coupled to the tank 220. The lifting eyes 228 are configured to receive a hook (not shown) for lifting the tank 220 with a crane 112 (FIG. 1). Additionally, the tank 220 has slots 230 that allow the tank 220 to be lifted or transported by, for example, a forklift. The lid 222 is coupled to the top 224 of the tank 220 by one or more hinges 226 (also shown in FIG. 4). As shown in FIGS. 3 and 5, the lid 222 is manually opened by standing on the top 224 of the skip 220 and lifting on the on the side 230 opposite the hinged 226 side.
As shown in FIG. 6, after the lid 222 on the skip 220 is manually opened, waste material and drill cuttings separated from the drilling fluid are discharged from a separator 232 into the skip 220. The separator 232 may be disposed in a structure 234 that allows the separator to be positioned above the skip 220. Once the skip 220 is full, as viewed through, for example, a portal 236 disposed on the top 224 of the skip 220, the lid 222 may be closed and moved to a storage location on the drilling platform 114 (FIG. 1) or to a ship 116 (FIG. 1) for transportation onshore. Corresponding locks 238 on the lid 222 and the top 224 of the skip 220 secure the lid in the locked position to prevent leaks or spills of the drill cuttings during transportation.
Typically, mud skips for offshore drilling rigs range in size from 15 barrel (bbl) containers to 25 bbl containers. The skips may be comprised of galvanized steel that is internally coated for corrosion resistance. A skip, when empty, may range in weight from approximately 3000 lbs (1300 kg) to 4500 lbs (2000 kg) or more. The size of a skip may also vary based on the space available on a drilling platform for storage and the amount of drill cuttings produced. For example, a skip may vary in size from approximately 7.5 ft long by 4.5 ft wide by 4 ft high to 8 ft long by 8 ft wide by 4 ft high or larger. Accordingly, the gross total weight and capacity of each skip varies due to the variation in empty weight and size of the skip. The lids of the skips are also extremely heavy so as to provide a greater seal of the skip opening. Typically, a lid may weigh several hundred pounds or more. The heavy weight of the lids and the position of the operator atop the skip often present a safety concern for personnel when opening and closing the lids. Further, the lids are typically only safely secured in a fully open or fully closed position.
Accordingly, there exists a need to effectively and safely seal and store drill cuttings and waste material in mud skips.